asks: How do I write an unexpected couple in a book? As in, the readers think she'll end up with the guy she initially likes, but she ends up falling in love with someone else?

Considering how popular it is for a main character to have two love interests, most readers can spot the outcome a mile away. Like with plot twists (See "Question 3: Plot Twists" for a refresher), you first have to lead the reader down a particular path. All the main character's attention is on the expected love interest. But in the background, the actual love interest will be quietly earning his place in her heart. They will have to be very subtle or hidden things, not grand gestures.

There should be a defining moment where she makes her decision. It can be a stressful event where each guy's true colors are shown. Or maybe she discovers all the hidden things that the unexpected guy has been doing. It can't be a flippant decision like choosing an ice cream flavor. She has to have a moment of clarity.

When she chooses the the unexpected person, there must be an explanation. Guide the reader through her reasoning, otherwise the readers are going to be scratching their heads and saying, "Why?? What just happened?" The character should make a mental tally of all the reasons this works better than a relationship with the other guy. Or why the other guy isn't right for her after all. Everything has to click into place. If there's still room for doubt, then the result won't feel very satisfying.

It has to make sense, or the reader isn't going to buy it.